- "Rule number one. We're not just here to make a cure, we're here to make a choice."
- —Cisco Ramon to Caitlin Snow[src]
The meta-human cure, also commonly referred to as the cure or the meta cure, is a serum created by Cisco Ramon and Caitlin Snow to remove a meta-human's powers by suppressing the dark matter in their pituitary gland. While Team Flash has plenty of the cure on hand, they swore to never use it as a weapon, and only administer it to meta-humans who give consent.
After Cisco Ramon's hands were injured by Orlin Dwyer/Cicada's dagger (which could negate the powers of meta-humans who gained their abilities from exposure to dark matter), he began having trouble using his powers. After removing small shards of the dagger from the wounds in his hands, Cisco decided to run some tests on the shrapnel and his hands' tissue, which revealed that the shards hadn't been dampening Cisco's powers but removing them. This inspired Cisco to use this information to make a meta-human cure.
At first, Caitlin Snow wasn't on board with the idea as she believed it wasn't necessary for a cure to exist; neither was Killer Frost, who sabotaged Cisco's first attempt at making the cure. When she did that, Cisco revealed that she ruined his only chance to have a normal life. Having a change of heart, Caitlin brought Cisco to her father's old lab in order to use his research to reverse the process of creating a meta-gene. In exchange for them working on it together, the two set up some rules, the most important one being that they will never force the cure on anyone.
Killer Frost still didn't agree with the creation of the cure so she continued to try and sabotage it by altering Caitlin's equations while Cisco was working in in the Tannhauser offsite. Caitlin later realized she needed a DNA sample from a meta-human who hasn't fully bonded with dark matter to make the cure. To get her point of view through to Caitlin, Killer Frost destroyed all of her equations before being recruited to help Team Flash locate meta-humans who were in danger from Cicada. After Ralph Dibny assured her that she doesn't be afraid of Caitlin making and possibly taking the cure, Killer Frost decided to help. She took some of Cicada's blood when fighting him and gave it to Caitlin.
Cisco kept working on the cure, seeing that something was missing. After being taken to a bar by Ralph, he started talking with Kamilla Hwang, who told him she had a sister. Cisco then realized that he needed DNA samples from siblings who were both exposed to dark matter where one of them became a meta-human and the other didn't. After locating a pair of siblings who fit this description for his research, Cisco informed Team Flash that the cure was as good as done. Barry then revealed he wanted to use the cure on Cicada.
Cisco sent a sample of the meta-human cure to Caitlin to test if it could work. Her test was successful and she sent it back to Cisco for final processing. Caitlin then revealed that giving the cure to Cicada wouldn't be that easy, since the effects aren't instant and take about a minute to work so they have to keep him still during that time. Caitlin had a solution for this; using a Neuro-Stasis Field Generator, which was located in Goldface's black market. Barry and Ralph tried to get their hands on the device, but failed. Luckily, Iris West-Allen learned about Orlin's lung injury, giving the team another way to administer the cure.
Cisco finished the cure but then found out that they had to wait 29 days before they could use the serum for it to completely synthesize. However, the process was sped up when Barry took the cure with him into the Speed Force, using its tachyons to synthesize the serum. When Barry returned, the meta-human cure was fully prepared and ready to use.
Now that the cure was ready, Team Flash needed to test it on a meta-human. After discussing their options, given that all the Earth-1 meta-humans they knew of had either been killed by Cicada or otherwise gone into hiding to stay safe from him, Team Flash began entertaining the possibility of asking Harry Wells if he knew of any Earth-2 meta-humans who'd be interested in serving as a test subject. They then realized that there was already a meta-human from Earth-2 on Earth-1 they could try asking, who most likely didn't want his powers; King Shark who was being held at A.R.G.U.S.. Due to an interference from Grodd though, King Shark escaped. When Team Flash found him again, Barry immediately used the cure on him, causing King Shark to return to his human form, Shay Lamden.
Back at S.T.A.R. Labs, Cisco and Caitlin were upset with Barry because he used the meta-human cure on Shay without asking for his consent. Suddenly, a problem arose with Shay's condition; since the cure was developed to work on the human part of a meta-human's brain, the animal part of Shay's mind had fought back, resulting in some residual dark matter remaining in his pituitary gland, which meant he wasn't going to be human forever. Caitlin made sure to adjust the cure so that it could work on him. However, Shay decided to give up the chance to be fully cured in order to save Central City from Grodd by changing back into King Shark. Afterwards, Barry apologized to Shay for using the cure on him and then came up with the idea to offer the cure to Cicada.
After discussing how they could give the cure to Orlin without having to fight him, the team tracked him down. Killer Frost made sure that Orlin wouldn't be able to use his dagger, allowing The Flash to talk to him. The Flash tried to convince Cicada to take the meta-human cure for the sake of his legacy but Cicada went on to fight him, declaring that he didn't care about his legacy. When confronted again, The Flash shared the news that Orlin's niece, Grace Gibbons, was also a meta-human. Following this revelation, Orlin came to an agreement with Team Flash that they first cure him and then Grace. Orlin was taken to S.T.A.R. Labs to be administered the cure, after which the wound in his chest was stitched up.
Prototypes of the cure were later stolen by a time-traveling future Grace, who'd become Cicada II. She attempted to use a Cryo-Atomizer to spread the prototype all over Central City to kill every meta-human. Since these prototypes are the imperfect, unfinished product, they had deadly effects when taken without proper treatment. To stop Grace's plan, Team Flash decided to distribute the cure to meta-humans who wanted to be safe at the CCPD. They cured an unknown number of metas, but some people, such as Renee Adler, decided to keep their powers. Later though, Team Flash stopped Grace's weapon and managed to convince her present-day self to take the meta-human cure, erasing Grace's serial killer future self from existence. As a result, Team Flash didn't have to distribute the cure anymore.
After Cicada II was defeated, Cisco decided to take the meta-human cure, desiring the chance to live a normal life with Kamilla.
Known meta-humans cured
Formerly cured meta-humans
- Shay Lamden/King Shark (needed a stronger cure; lost the chance to be cured again after turning back into King Shark)
- Given the fact the cure works by removing the dark matter from the subject's system, it won't have any effect on meta-humans that were created otherwise, such as Killer Frost.
- Most likely unaware of this, Killer Frost sabotaged Caitlin's efforts to work on the cure multiple times, because she was afraid that Caitlin may someday decide to take the cure and Killer Frost would vanish as a result, leaving Caitlin with no one to protect her.
- According to Cisco and Caitlin, the cure works by suppressing the dark matter in the subject's system, rather than completely removing it. Thus, the drug's effects may be reversible.